Display systems based on coherent arrays of optical fibers have been developed to replace more cost/performance-limited conventional large display systems. The fiber-optic-based display systems can present static or animated images and are well suited for a variety of applications such as advertising and entertainment. These fiber-optic matrix displays offer significant advantages over other, more conventional displays that use light bulbs, LEDs, CRTs, flip disk type mechanisms, or projection systems. These advantages include, for example, lower weight, greater energy efficiency, superior color fidelity, and lower costs of manufacturing, transportation or delivery, operation, and maintenance.
Fiber-optic displays typically employ a source of illumination and an imaging medium such as film transparencies, motion picture film, or transmissive light-valve devices such as liquid crystal panels to generate source images. Light from the illumination source is directed through the imaging medium to an input matrix that holds input terminals of plural elongate optical conductors. The input terminals are mounted in closely packed rows and columns having relative positioning that corresponds with the relative positioning of spaced-apart rows and columns of output terminals of the optical conductors held in a much larger display matrix. Thus, the light delivered to the input terminals is carried along the optical conductors and delivered to the output terminals to form a display image having a greater size than the source image. One such display system is described in International Publication No. WO 93/06584, published on Apr. 1, 1993.
Large displays are often divided into smaller segments or panel sections to reduce costs by easing manufacturing requirements and by simplifying packaging or transportation. Individually providing each panel section with a light source and an imaging medium creates brighter displays that offer increased contrast and viewing distance. Upon installation, these sections are preferably arranged and fixed adjacent to one another so that seams or voids between the sections are eliminated. The imaging media are arranged in communication with the sections to generate a cohesive image when the individual panel sections are illuminated simultaneously. This technique is referred to as tiling.
One disadvantage of tiling is that non-uniform illumination of the separate input matrices will visually delineate the smaller panel sections and spoil the illusion of a single, large display. In addition, the range of point-to-point brightness variations within each of the panel sections contributes to even more substantial point-to-point brightness variations in the larger composite display. An illumination system of a display system should, therefore, efficiently and uniformly couple the high intensity light or luminous energy provided by the light source through the imaging media into the input matrix. The coupling efficiency is largely a function of the angles by which light rays enter the fiber optics.
First, the internal reflection inherent to the cladded optical conductors imposes a critical acceptance angle on the light entering the input terminals of the optical conductors. Thus, light rays impinging on the input terminal of an optical conductor at angles greater than the critical acceptance angle will not be reflected back into the fiber core by the interface formed by the core and cladding and will not propagate through the optical conductor.
Moreover, conventional illumination systems, which may employ ellipsoid reflectors, typically utilize less than 50% of the full acceptance angle of the optical conductors. Thus, optical losses occur because the collecting optics of conventional illumination systems do not efficiently direct luminous energy emitted from the light source into the fiber-optic input matrix. Furthermore, the optical conductors are not straight in most practical applications, but experience curves and bends through wide angular variations that create additional losses.
By providing illumination through only a portion of the entire acceptance angle of an optical conductor, fewer propagation modes become available to the light energy. This increases the statistical likelihood of losing a light ray traveling through the optical conductor due to geometric imperfections and reduces the amount of light energy ultimately conducted by the optical conductor. These losses, combined with non-uniform illumination patterns created by conventional optics, yield lower display intensities and often result in point-to-point variations in display brightness of greater than 60%.